Method and apparatus for calibrating the position of a tool and for gauging the dimensions of a workpiece

ABSTRACT

In a machine tool, a calibration and gauging system comprising drive means for moving a tool or inspection probe to a commanded position which is beyond a calibration position. The calibration and gauging system also includes circuitry for developing a transfer signal when the tool or inspection probe has arrived at the commanded position and a &#39;&#39;&#39;&#39;false&#39;&#39;&#39;&#39; transfer signal when the tool or probe has arrived at the calibration position. The transfer signals initiate the next sequence of the machine tool program.

United States Patent Kinney 1 Feb. 15, 1972 [54] METHOD AND APPARATUSFOR [56] References Cited CALIBRATING THE POSITION OF A UNITED STATESPATENTS TOOL AND FOR GAUGING THE DIMENSIONS OF A WORKPIECE ttwopdl..,....90/8

, ice e a [72] Inventor: John M. Kinney, Cortland, Ohio 3,447,419 6/1969Foster ...90/l3 C [73] Assigneez The American welding & Manufacturing3,481,247 12/1969 Hayes ..90/1l Company warren Ohm PrimaryExaminer.lames M. Meister [22] Filed: Aug. 13, 1970 Attorney-Watts,Hoffmann, Fisher & Heinke [21] Appl. No.: 63,620 [57] ABSTRACT RelatedUS. Application Data in a machine tool, a calibration and gauging systemcomprising drive means for moving a tool or inspection probe to a [63]fggg of commanded position which is beyond a calibration position. Thecalibration and gauging system also includes circuitry for developing atransfer signal when the tool or inspection probe [52] US. Cl ..82/l,82/2, 82/21, has arrived at the commanded position and a transfer 90/13318/572 signal when the tool or probe has arrived at the calibration g 2position. The transfer signals initiate the next sequence of the re 0are machine tool program.

28 Claims, 9 Drawing Figures l 185x L? 18c 70 GATEISO I PMENTEUFEB 15I972 CONTACT SENSOR FROM TAPE SHEET 1 OF 6 [42 ERRoR D7gCT/VA To DETECmRCIRC/ZIJITRY MACH/N5 INDICATOR VISUAL /30 C/RCU/TR READOUT 28 TOAND FROM52 MACH/NE f" RECORDER T0 M00E SW/TCH 5-1 \a f 0 17%. 1 -18c 247 70 GATE/50 INVENTOR. JOHN M K/NNEY jwwm A TRDRNEY:

METHOD AND APPARATUS FOR CALIBRATING THE POSITION OF A TOOL AND FORGAUGING THE DIMENSIONS OF A WORKPIECE This application is acontinuation-in-part of US. Pat. application Ser. No. 776,389, entitled,Method and Apparatus Including a Gauge for Positioning a NumericallyControlled Machine" and filed on Nov. 18, 1968.

BACKGROUND OF THE INVENTION This invention relates to machine tools, andmore particularly, to a method and apparatus for accurately positioninga tool or an inspection probe with respect to a calibration position inorder to eliminate machining and inspection errors due to tool orinspection probe wear, incorrect dimensions of the tool or probe,misalignment of the tool or probe, etc.

The operation of numerically controlled machine tools is now awell-known operation and extensively utilized in the field of machining.Briefly, this operation comprises moving a tool or a workpiece inaccordance with numerically programmed instructions. The instructionsdetermine the path of travel of the tool, which may be linear orcircular. Signals indicative of the position of the tool at any giventime are compared with signals derived from the programmed instructionsthat determine the path of the tool, and the tool continues moving untilthe two signals are alike. When the two signals are alike, indicatingthat the tool has arrived at a commanded position, a transfer signal isprovided to indicate that the tool is ready to execute a new command.Normally, the commands are supplied as signals that indicate a newposition to which the tool is to move, and a signal that indicates therate of speed at which the tool is to move to that new position. For adescription of the fundamentals of numerical control,-

reference may be had to a publication entitled, Numerical Control, by R.M. Dyke, Prentice-Hall, Inc., 1967.

In present day applications it is often necessary to machine a largepart with extremely small dimensional tolerances. For example, in oneapplication it is necessary to contour the outer surface ofa ring 36inches in diameter to various dimensions that must be accurate to within:0.00l inch. Such a part may be a component of a jet engine whereextreme accuracy in machining is vital. Heretofore, this has been atime-consuming operation, because after each cut made by the tool theworkpiece had to be dimensionally gauged. An initial dimensional gaugingoperation was required after the first cut in order to correct forincorrect dimensions of the tool, misalignment of the tool in itsmounting or the like. Gauging was necessary after subsequent cuts inorder to correct for wear of the tool. When any of these errors weredetected by manually measuring the dimensions of the workpiece, thecommands or instructions to the tool were varied from the preparedprogram by amounts sufficient to compensate for the errors. This is timeconsuming, inasmuch as it requires stopping the machine tool and havingan operator perform the gauging operation, determine the amount ofoffset or correction that must be provided to correct the program, andset that correction factor into the control system. Not only has thisprocess been time consuming, but it provides opportunity for human errorin setting the correct offset to the computer. It has been found fromexperience that numerous expensive workpieces must be scrapped becauseof that human error.

Hereinafter, for the sake of clearness of description, reference will bemade to a machine tool in which an operating tool moves relative to aworkpiece. It is understood, however, that the invention is equallyapplicable to a machine tool in which the operating tool is fixed inposition and the workpiece is moved relative to the operating tool.

Accordingly, it is a general object of the present invention to providea method and apparatus whereby the operative or functional edge of atool may be accurately positioned with respect to a calibration positionin order to eliminate machine errors due to the foregoing reasons, andconsequently to eliminate the needs for manually gauging the dimensionsof a workpiece during the machining process and for manually inspectingand dimensionally gauging the workpiece after machining is completed.

Some gauging of critical parts after the machining is still frequentlyrequired, therefore it is another object of the present invention toprovide a method and apparatus for accurately gauging the dimension ofthe workpiece.

SUMMARY OF THE INVENTION In certain types of numerically controlledmachine tools, a signalis provided which causes the tool to move from astarting position by a certain number of units of distance and at acertain rate of speed. When the tool has arrived at a predeterminedposition, a transfer signal is provided to the control circuitryindicating that the tool has executed the command and is ready toexecute a new command. The control circuitry then commands the tool tomove by a certain amount necessary in a direction or directions toattain a new position. The initial commands are based on the assumptionthat the tool length and the radius of the edge are as specified by themanufacturer, and that the tool is properly aligned in its mounting. Aswas pointed out, this is not necessarily correct.

According to the present invention, a calibration block is provided thathas surfaces which are parallel to the X and Y movement coordinates ofthe machine. The positions of these surfaces in the X- and Y-eoordinatesare very accurately known. The machine is commanded by a program tobring the tool into a position adjacent to one of these surfaces. Forexample, assume that the tool is commanded to move along an X orhorizontal axis until it is directly over the upper surface of the blockthat is parallel to the X-axis. It is then commanded to move downwardlyalong the Y-axis to a position at which, if attained, the tool wouldtravel through the X or horizontal surface of the block, i.e., to aposition which would be within the calibration block. When the operativeor functional edge of the tool comes into contact with the upper surfaceof the calibration block, a false transfer signal is generated and sentback to the control circuitry. This signal indicates that the tool hasreached the commanded position. At the instant this signal is developed,motion of the tool is stopped, and the program commands the tool to moveupwardly again and out of contact with the block.

Inasmuch as the position of the surface of the block that has beencontacted by the operative or functional edge of the tool is accuratelyknown, the position of the operative or functional edge of the tool atthe instant when it contacts the block is accurately known. Therefore,the program will control future positions of the actual edge of the toolreferenced to that calibration point in the direction of the Y-axis. Theoperation can be repeated for calibrating the position of the memberalong the X-axis using a surface of the calibration block that isparallel to the Y-axis.

The positionable member need not necessarily be a cutting tool, but maybe a probe or the like used in dimensionally gauging workpieces thathave been partially or completely machined.

For example, when the method and apparatus of the invention are used forgauging dimensions of a workpiece, the operating tool comprises a probehaving a noncutting tip for contacting a workpiece to be gauged. Theposition of the contacting portion of the probe is first determined bycalibration with respect to a calibration block as previously described.When the probe is calibrated, a counter is preset to the position of thesurface of the calibration block contacted. The probe is then commandedto travel beyond the surface of the workpiece to be gauged, i.e., to aposition which would be within the workpiece. When the probe contactsthe surface of the workpiece, a readout device presents a visual displayof the exact position of the probe and the probe is commanded to move toanother inspection position.

In the foregoing manner, all machining errors in a machine toolapplication due to wear of the edge of the tool, misalignment of thetool, incorrect length of the tool, etc., are automatically eliminated.Also, less precise and hence less expensive tools may be used withoutintroducing machining errors, and the number of different tools requiredfor a job may be reduced. The calibrating operation may be performed asmany times in the course of machining a workpiece as is deemednecessary.

In the case of a simple machining operation, calibrating may benecessary only once or twice during a complete machining operation. Thismay also be the case if relatively large dimensional tolerances arepermissible. On the other hand, if the part being machined has anintricate contour and many cuts are involved, or if the permissivedimensional tolerances are extremely small, the tool may be calibratedafter each cut. The calibrating process takes only a matter of seconds,which time is in no way comparable to the time necessary for an operatorto manually gauge the dimensions of the part being machined and adjustthe computer to compensate for dimensional variations.

Also, by utilizing the present invention, it is possible to accuratelygauge the dimensions of a workpiece with an inspection probe which isautomatically calibrated in the same manner as the tool, and whichautomatically travels to and gauges the dimensions ofa workpiece.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view and electricalschematic diagram illustrating a portion of a preferred embodiment ofthe present invention in conjunction with a conventional machine tool;

FIG. 2 is a much simplified block diagram illustrating the preferredembodiment of the present invention in conjunction with a machine tool;

FIG. 3 is a more detailed block diagram ofa machine tool to which theinvention may be applied;

FIG. 4 is a fragmentary view of a punched paper tape for providingnumerical input data to the machine tool shown in FIG. 3;

FIG. 5 is a block diagram of a distance counter shown in FIG. 3;

FIG. 6 is a logic diagram of a data transfer circuit shown in FIG. 3;

FIG. 7 is a timing diagram relating to the signals produced by the datatransfer circuit shown in FIG. 6; and

FIGS. 8 and 8a are logic diagrams of the circuitry of the preferredembodiment and the electrical connections between this circuitry and thecircuitry shown in other figures.

DESCRIPTION OF A PREFERRED EMBODIMENT The invention will be described inconnection with a numerically controlled vertical turret lathe. However,it is to be understood that the application of the invention is notlimited to any particular class of machine tool. It is applicable to anynumerically controlled machine tool where a calibration position of amovable tool or an inspection probe must be accurately determined inorder to reposition that element in successive steps with extremeaccuracy using the calibration position as a mounted, or if thespecified radius has changed because of tool wear, improper positioningof the tool will result. Once the tool has been used, the only positionthat is known mathematically is that of the center 12a of the radius ofcurvature of the tool edge. This has lead to the time-consumingdimensional gauging operations previously discussed.

The invention contemplates the provision of a calibration block 18having a horizontal upper surface 18a, and vertical side surfaces 18b,180. The calibration block 18 is precisely dimensioned and positioned sothat the position of its upper surface 18a is precisely known in theY-direction, and the positions of its side surfaces 18b, 180 areprecisely known in the X-direction. The block 18 is made ofa conductivematerial or has a conductive coating thereon and is insulated from theremainder of the machine by an insulating material 20. The block 18 isconnected to control circuitry to be later described by means ofa lead22.

The block 18 may be either movable or fixed in position. As shown, it ismounted on a slide 24 so that it may be moved out of the way of the toolwhen the block is not in use.

In practicing the calibration method of the invention, the

' tool 12 may be commanded to move to the position as shown reference.FIG. I illustrates a vertical turret lathe in which a ring 10 is mountedfor machining by a tool or inspection probe 12. The tool isconventionally mounted in a holder 14. The tool 12 is adapted to bemoved under numerical control vertically along a Y-axisand horizontallyalong an X-axis. As is apparent, the operating tool may also move inother directions that are combinations of movement in the X and Y-directions.

The term operating tool" will be utilized hereinafter in thespecification to include a tool, such as a cutting tool, or aninspection probe.

The dimensions of the tool 12 are provided by the manufacture andinclude the length of the tool to a center 12a of radius of curvature ofits edge 12b and the radius of the edge. If these dimensions areaccurate and the tool is properly mounted, the exact position ofthe tooledge can be determined. However, if the stated dimensions are incorrect,if the tool is improperly with its edge 12b above the surface 180. It isthen commanded to move downwardly in the Y-direction toward a level,such as is indicated at 26, which is located within the block 18. Whenthe edge 12!) of the tool 12 contacts the surface 18a, an electricalsignal is sent to the control circuitry over the lead 22. Because theblock 18 is precisely dimensioned and positioned, the exact position ofthe edge of the tool in the Y-coordinate is known at the time the signalis sent over the lead 22. The tool is then retracted to the originalposition as shown in FIG. 1. It may then be moved to the rightdownwardly in the Y-direction to the position shown in broken lines inthe figure. It would then be commanded to move to the left in theX-direction until the edge 12b of the tool touches the side 186 of theblock 18. At that time, another transfer signal is sent over the lead 22which serves to accurately locate the edge of the tool in theX-coordinate.

After the tool has been positioned as described, it is ready to executeits programmed instructions. The calibrating process may be repeated asoften as the complexityof the machine operation requires. If the partbeing machined has a relatively simple contour and hence requires fewmachine cuts, or inspections, it may be sufficient to calibrate the toolonly before starting the machining or inspecting operation. On the otherhand, if the part being machined has a relatively complex contourrequiring many operations, it may be desirable to calibrate the toolafter each cut or inspection. This matter is entirely under the controlof the programmer who programs the calibrating operations into themachine program.

FIG. 2 is a simplified block diagram illustrating the circuitry of theinvention applied to a conventional numerically controlled machine. Theconventional numerical control circuitry of the machine, which will belater described in. detail, is represented in FIG. 2 as a block 28. Asis well known in the art, the circuitry 28 provides signals to themachine to move the tool by a programmed number of increments ofdistance from one position to another position. When the tool hasreached the commanded position, a transfer signal is sent back to thecircuitry 28 indicating completion of that command. The circuitry 28 mayalso provide signals to a visual readout display 30 which indicates theinstruction or command being executed or which indicates the dimensionof the inspected point. If desired, these signals may be recorded by aprintout mode gate, further instructions on the tape cause the tool tomove as previously described with reference to FIG. I. When the toolcontacts the surface of the calibration block 18, a signal is sent onthe lead 22 to a contact sensor gate 38. This causes a contact signal tobe sent along with the enabling signal to the permit gauge transfer gate36. Coincidence of those two signals causes the permit gauge transfergate 36 to provide a false transfer signal to the numerical controlcircuitry 28. In effect, the false transfer signal tells the numericalcontrol circuitry that the tool has executed a given command when, infact, no command has been executed. However, inasmuch as the exactposition of the tool is known in one coordinate at the time the falsetransfer signal is provided from the permit gauge transfer gate 36 t0the numerical control circuitry 28, the program can, in effect, berestarted from that particular known position.

The diagram of FIG. 2 also includes anerror detector gate 40. The errordetector gate 40 serves to provide a signal to deactivation circuitry 42to deactivate the machine under either of two abnormal conditions, andto provide signals to indicators 44 that visually or audibly indicate amalfunction. At one pair of inputs, the error detector gate 40 receivessignals from the gauge mode gate 34 and from the contact sensor gate 38,and will provide an output signal if the tool improperly touches thegauge when the machine is not in its gauge mode of operation. At anotherpair of inputs, the error detector gate 40 receives signals from thenumerical control circuitry 28 and from another output of the gauge modegate 34. The error detector gate 40 will provide a deactivation signalto the circuitry 42 if, during a gauging mode of operation, a normaltransfer signal'is provided from the circuitry 28. This condition mightoccur if the tool being gauged is too short, if the gauge is of impropersize, or if there is a program error. In any of these cases thecircuitry 42 will deactivate the machine and energize the indicators 44.

FIG. 3 is a simplified block diagram of a typical numerical control towhich the invention may be applied. Inasmuch as the control shown inFIG. 3 is well known, it will be described only in such detail as isnecessary to enable one to have a full understanding of the presentinvention.

The basic function of a control system such as that shown in FIG. 3 isto provide continuous coordinated position control of two or moremachine motions or axes. For such a control, it is necessary to generatefor each of the controlled axes a continuous position command signal"and to provide a continuous feedback indication position feedback signalof the actual machine position.

In the illustrated system, the position command signals and the positionfeedback signals are both in the form of phaseanalog" voltages. Eachphase-analog voltage is a single-phase, alternating-current voltagehaving a nominal frequency of 250 hertz. Such a voltage conveys positioninformation by means of its phase relationship to a master 250-hertzreference voltage provided in the system. To indicate a change ofposition, the phase-analog voltage shifts in phase by an amountproportional to the position change.

The operation of the entire system is governed by a square wave,250-kilohertz clock signal produced by a crystal-controlled clockoscillator 50. The 250-kilohertz square wave is provided from the blockoscillator 50 to a reference counter 52, where it is counted down toproduce a 250-hertz square wave which serves as the reference voltagefor all motions in the system.

To develop the phase-analog voltage which provides the position feedbacksignal, the 250-hertz reference voltage is provided to a resolver supply54, which converts the reference voltage to 250-hertz sine and cosinevoltages. These serve as a source of two-phase excitation for anX-position resolver 56 and a Y-position resolver 58. When a resolver isexcited by a two-phase source, there is induced in its output winding asin gle-phase sinusoidal voltage, which shifts in phase relative to thereference voltage as a function of the resolver shaft position. Theshafts of the resolvers 56, 58 are respectively connected mechanicallyto the tool whose position is being sensed. Thus, a sinusoidalX-position feedback signal is provided from the resolver 56 to a waveshaper 60, which converts the sinusoidal signal into a square wavehaving the same phase relationship to the reference voltage as did thesinusoidal wave. A Y-position feedback signal is similarly shaped into asquare wave by a wave shaper 62.

The phase-analog voltage which serves as the X-position command signalis produced by feeding the 250-kilohertz output signal of the clockgenerator 50 to an X-command phase counter 64. In its simplest action,the phase counter 64 counts down the ZSO-kilohertz signal to produce a250-hertz square wave output signal much as the reference counter 52does. A similar phase-analog voltage which serves as the Y-positioncommand signal is produced by a Y-command phase counter 66.

The relative phases of the X-position command signal from the X-comrnandphase generator 64 and the X-position feedback signal from the waveshaper 60 are compared in an X- phase discriminator 68. Thediscriminator 68 in cooperation with an X-operational amplifier 70develops a position error signal, whose magnitude and polarity are afunction of the relative phase displacement between the two inputsignals to the discriminator. This X-position error signal causes an X-motor control 73 to drive an X-drive motor 74, which drives the machineand the resolver 56 in a direction to reduce the position error signaland the phase displacement between the two phase discriminator inputsignals. Similar circuitry for generating a Y-position error signalcomprises a Y-phase discriminator 76, a Y-operational amplifier 78, aY-motor control 80, and a Y-drive motor 82. The Y-components function inexactly the same manner as the X-components previously described.

The positioning control thus far described would function merely to holdthe machine at a fixed position and act to bring it back to that fixedposition if it were disturbed. In order to produce controlled motion ofthe machine, the cyle-counting actions of the command phase counters 64,66 must be modified to cause phase shifts of the position commandsignals, so that their rate of phase shifts and the total phase shiftsare proportional to the desired velocity and total displacement of thecontrolled motion. For this purpose, the command phase counters 64, 66are designed to accept second input signals in the form of controlpulses. The effect of one control pulse applied to a command phasecounter is to modify the normal counting action of the countermomentarily so as to produce a small shift in phase of its outputsignal. Regular repeated applications of control pulses produce repeatedshifts in phase of the position command signals in increments equivalentto 0.0001 inch of machine motion, giving the effect of a continuousphase shift at a rate proportional to the frequency of the appliedcontrol pulses. The source of control pulses for the phase counterscomprises a manual feed rate override circuit 84, a contouring velocitycontrol 86, and a function generator 88.

The manual feed rate override 84 is driven by a I25- kilohertz squarewave input signal provided from an intermediate point within thereference counter 52. This signal is hereinafter called CL. If fed as astream of pulses directly into the command phase counters 64, 66, itwould produce a maximum permissible feed rate for the system. To permitcontrolling the motion in the system at a feed rate lower than itsmaximum, the signal CL is not fed directly to the command phase counters64, 66, but is reduced in frequency by passing it through the manualfeed rate override circuitry 84, the contouring velocity control 86, andthe function generator 88. Each of these components is capable ofreducing the frequency of its incoming train of pulses and supplying tothe next component of the system a train of approximately equally spacedpulses occurring at a reduced pulse repetition frequency. By thecombined action of those three components, the command phase countersare supplied with streams of control pulses suitable for commanding thedesired feed speed.

Input information for the system is provided from a numerical data inputcircuit 90. Contouring instructions are supplied to the control asblocks of data, each of which specifies a straight line or circular arcpath. The data is read from a numerical input medium, such as punchedpaper tape, by a tape reader and transferred to buffer storage elementsincluded within the various other components of the system. Normally,while the control is processing one block of data, the tape readerstarts and quickly reloads the buffers with new information for thefollowing block. Upon completion of the processing of a given block ofdata the new instructions are transferred from the buffer to the activestorage in response to a transfer signal, and computation on the newdata block is initiated. input data is sent from the input circuitry 90to the contouring velocity control 86, to the function generator 88, tothe X-command phase counter 64, to the Y-command phase counter 66, to anX-distance counter 92, and to a Y- distance counter 94.

Referring again to the source of control pulses for the command phasecounters, it is pointed out that the basic function of the manual speedrate override circuitry 84 is to provide the machine operator with amanual means of increasing or decreasing the feed rate from theprogrammed rate. The contouring velocity control 86 is a pulse ratemultiplier, which multiplies the pulse rate of its input signal by onefive-hundredth times a decimal numerical command received from thenumerical data input circuitry 90.

The function generator 88 is actuated by an incoming pulse train fromthe contouring velocity control 86 and, under control of data receivedfrom the numerical data input circuitry 90, discharges pulses to theX-command phase counter 64 through the X-distance counter 92 and to theY-command phase counter 66 through the Y-distance counter 94. Thefunction generator 88 performs two basic functions. It is designed towork in a single plane at any one time, and it puts out pulse trainscommanding motion along:

a. a straight line of positive slope and any length within the capacityofthe generator; or

b. an arc of any length within one quadrant of a specified plane. Thefunction generator output consists of two pulse trains, DF and UP. Thepulse frequencies of these trains control the velocities of movement ofthe tool in the X-direction and Ydirectin, respectively, to give therequired resultant velocity along the contouring direction. Also, thetotal numbers of such X or Y-axis impulses control the distance oftravel.

The X-axis and Y-axisdistance counters 92, 94 respectively measure thedisplacements of the X- and Y-command signals by counting the outputpulses received from the function generator. When the total number ofcounter pulses received from the numerical data input circuitry 90reaches a commanded number, the distance counters prevent the flow ofpulses to their respective command phase counters 64, 66, whichindicates that the X- and Y-counts have been completed. When bothdistance counters 92, 94 have indicated that the count is complete, adata transfer operation is initiated by a data transfer circuit 96. Thedata transfer circuit 96 applies a transfer signal TF to operatetransfer gates of all buffers and counters to cause a new block of datato be transferred from buffer to active storage, applies a transferreset signal TRS to the function generator 88 and to the distancecounters 92, 94, applies a blocking signal TB to the function generator88 and to the counters 92, 94 to suspend operation of those units, andapplies a buffer reset signal BR to the function generator and thedistance counters. The data transfer circuit 96 can also be actuated byreceipt of a signal from the permit gauge transfer gate 36 as shown inFIG. 2. It is this latter signal that falsely indicates that the machinehas attained a commanded position and is used in the calibratingprocess, as heretofore described.

The numerical data input circuitry 90 includes a tape reader and variousconventional recognition and decoding circuits. The data input circuitry90 operates to read coded data from a punched paper tape, such as thatshown in FIG. 4, and route the decoded information to the variousspecified components in the control. A typical paper tape is 1 inch wideand information is put on the tape by holes punched in longitudinalTracks l-8 and transverse Rows 0-5. Each row across the tape representsa character, and the number and position of the holes form a code whichidentifies the character. In the present example, Tracks 1-4 identifynumbers. Track 5 is used for a parity check of conventional type. Tracks6 and 7 are used in conjunction with Tracks l4 to indicate letters.Track 8 is exclusively used for a signal (EOB) indicating the end of aninformation block. Sprocket holes are punched between Tracks 3 and 4.

Row 0 contains an address letter, and Rows l-5 contain numbers thatindicate a tool position movement from O9.9999 inches, in a directioncommanded by the letter in Row 0. For example, Rows 05 might containX35217," which would command the tool to move in the X-direction by3,5217 inches. This is conventional and well known in the art. The Rowsl-5 are counted, and signals provided indicating which row after Row 0is being decoded.

The X-axis distance counter 92 is shown in FIG. 5. The Y- axis distancecounter 94 is essentially identical to the X-axis distance counterexcept for axis nomenclature and input selection signals. Therefore onlyone of the two distance counters is shown. As shown, the distancecounter is a fivedecade decimal counter with associated buffers. It hasa capacity of 099,999 increments equivalent to 0-9.9999 inches. In FIG.5, the five decades of the counter are labeled a-100e, and thecorresponding buffers are labeled 102a102e. The departure distancecommand for the axis is read into each decade of the buffers 102 asindicated by signals Tl-T4 from Tracks 1-4, when the X-axis commandsignal is read from the paper tape. The five buffers 102a-102e alsorespectively and sequentially receive signals Rl-RS from a row counter(not shown) embodied in the numerical data input circuit 90. Thus, asthe tape is read, the buffers 102a-l02e are sequentially filled withinput data. At the time of completion of a command from a previousblock, a transfer signal TF is provided to the counter sections100a-l00e, which transfers the distance command from the buffers to thecorresponding counter sections. The distance counterthen countsdownwardly from the preset distance count to zero. The least significantfigure section 100s of the counter receives clock pulses CL. The decadesof the counter are so connected together that for each countdown of 10in one decade a single pulse is applied to the next more significantfigure decade to cause it to count down by one unit. Each decadel00a-l00e of the counter also receives transfer reset signals TRS andtransfer blocking signals TB from the data transfer circuit 96. Eachbuffer l02a-l02e also receives a buffer reset signal'BR from the datatransfer circuit.

The distance counter also includes input selection gates comprising twoAND-gates 104, 106 and an OR-gate 108. The AND-gate 104 receives a trainof signals UF from the function generator 88, and the AND-gate 106receives a train of signals DF from the function generator 88. One orthe other signals UF, DF will be provided depending on the direction ofmotion that is being commanded. A second input to each of the AND- gates104, 106 is received from the output of an AND-gate 110. The AND-gatehas five inputs which are respectively connected to outputs of thecounter decades 100a-l00e. When the counter has counted down to zero,the AND-gate 110 is enabled. This provides an output signal DXO to thedata transfer circuit 96, which signal also blocks the AND- gates 104,106. Before the counter has counted down to zero, one or the other ofthe AND-gates 104, 106 will be enabled and a contouring increment signalPCX will be passed by the OR-gate 108 and provided to the X-commandphase counter 64. That signal is also provided to a steering input ofthe first decade 100a of the distance counter to simultaneously producea decrease of one count in the counter and a phase shift of oneincrement in the command phase counter, when the next following clockpulse CL is received.

FIG. 6 is a logic diagram of the data transfer circuit 96 shown in blockdiagram form in FIG. 3. Basically, it comprises a transfer resetflip-flop 112 and a transfer flip-flop 114, with various input andoutput gates. The transfer of data from buffer storage to active commandis normally initiated as soon as both axis distance counters 92, 94 havereached zero, indicating the completion of motion on a given block ofdata. However, that transfer of data can also be initiated in accordancewith the present invention by providing a false signal to the datatransfer circuit, which falsely indicates a completion of motion on agiven block of data.

The transfer of data entails four operations. The operations are, in theorder of occurrence, transfer blocking (TB signal), transfer reset (TRSsignal), transfer (TF signal), and buffer reset (BR). These signals beara synchronous relationship to the clock signal CL, and are connected tothe data storage Iocations to produce a coordinated, parallel transferof data. The time relationship of those signals is shown in FIG. 7.

The transfer blocking signal TB suspends operation of the functiongenerator 88. It also turns off the count gates of all but the leastsignificant decade l02e of the distance counters 92, 94 in order toprevent a progressive triggering from one decade to the next during thetransfer reset operation.

The transfer reset signal TRS resets both distance counters 92, 94 inpreparation for the next operation.

The transfer signal TF operates the transfer gates on all active commandbuffers and counters to bring the flip-flops in both counters 92, 94into agreement with the states of the corresponding flip-flops in theirbuffers, and thereby effect the actual transfer of data.

The buffer reset signal BR resets the buffers in the distance counters92, 94 so that programmed distances are wiped out after once being used.Buffer values for new distances are then zero until new values are readin.

Input to the data transfer circuit is'through an AND-gate 116. TheAND-gate 116 receives DXO and DYO signals from the distance counters 92,94, respectively, and a steering signal from the reset flip-flop 112.Output-of the AND-gate 116 is to one input of an OR-gate 118. A secondinput of the OR-gate 118 is connected to receive the output from thepermit gauge transfer gate 36 shown in FIG. 2. The output of the OR-gate118 is connected to one input of an AND-gate 120, and a second input ofthe AND-gate 120 receives inverted clock pulses CL. An output of theAND-gate 120 is connected to a set input terminal of the reset flip-flop112. The output of the OR-gate ll8provides set steering for the resetflip-flop 112. The flip-flop 112 is reset by an output signal from anAND-gate 122. One input of the AND-gate 122 receives clock pulses CL,and a second input of that AND gate receives a steering signal from theoutput of the transfer flip-flop 114.

The transfer flip-flop 114 receives a set input signal from an output ofan AND-gate 124. One input of the AND-gate 124 receives a signal fromthe reset flip-flop 112, and a second input of that AND gate receivesclock signals CL. The signal from the reset flip-flop 112 providessteering for setting the transfer flip-flop 114. A reset input of thetransfer flip-flop 114 is connected to an output of an AND-gate 126. Oneinput of the AND-gate 126 is connected to receive clock pulses CL, and asecond input of that gate is connected to receive an output signal fromthe transfer flip-flop 114. The signal from the flip-flop 114 providesreset steering for that same gate.

The output gates of the data transfer circuit comprise three AND-gates128, 130, 132 and an OR-gate 134 followed by an inverter 136. TheAND-gate 128 is connected to receive TRG and TFG signals from the resetflip-flop 112 and the transfer flip-flop 114, respectively, and providesthe signal BR. The AND-gate 130 likewise receives signals from those twoflipflops, but the signals are of opposite polarity (TRG and TFG) tothose supplied to the AND-gate 128, and provides the signal TRS. TheAND-gate 132 also receives input signals from those two flip-flops, butthe signals have different polarity relationships (TRG and TFG) thanthose supplied to the other two AND gates, and provides the signal TF.The OR- gate 134 receives signals (TRG) from the reset flip-flop 112 andsignals from the output of the input AND-gate 116. The output signal ofthe OR-gate 134 is merely inverted by the inverter 136 to provide thesignal TB.

In the operation of the data transfer circuit, the reset flipflop 1 12and the transfer flip-flop 114 are initially both in reset states. Whenthe DXO and DYO input signals to the AND- gate 116 go to logic 0,indicating that the distance counters 92, 94 have counted down to zero,an output signal from the AND-gate 116 causes the transfer blockingsignal TB to go to logic I. This action also causes the reset flip-flop112 to be set steered.

The next incoming CL signal through the gate sets the flip-flop 112.Thus, its output signal TRG goes to logic I" and acts through the gates134, 136 to hold the output signal TB at logic I. Since the resetflip-flop 112 is set and the transfer flip-flop 114 is reset, theiroutput signals act through the AND-gate to cause the signal TRS to go tologic "1. This resets all of the flip-flops in the distance counters 92,94 which causes the signals DXO and DYO to go to logic I and removes theset steering signal from the reset flip-flop 112.

The next incoming CL pulse sets the transfer flip-flop 114, since thesignal TRG is at a logic zero and provides the proper steering. Thesignal TRS then goes to logic since that signal can be at logic 1" onlywhile the reset flip-flop 112 is set and the transfer flip-flop 114 isreset. Simultaneously, the signal TF goes to logic 1, since it can be atlogic l only when both flip-flops 112, 114 are set.

The next clock pulse CL resets the reset flip-flop 112. The flip-flop112 was steered to reset when the flip-flop 114 was set. Therefore, theoutput signal TF goes to logic 0 and the output signal BR goes to logicl The next clock pulse CL resets the flip-flop 112, thus causing thesignal BR to go to logic 0.

The next clock pulse CL resets the flip-flop 112, thus causing thesignal BR to go to logic O." The output signals TRS, TF, and TB havepreviously gone to logic 0. The flip-flops 112, 114 are both reset andthe transfer cycle is completed.

In accordance with the present invention, the same data transfer actionis initiated by providing a logic 1 signal to the OR-gate 118 from thepermit gauge transfer gate 36 (FIG.

2), when the gauger of the invention is made operative.

FIGS. 8 and 8a are logic diagrams of exemplary circuitry embodying theinvention and showing the interconnections with the other portions ofthe control circuitry. Those sections of the circuitry shown in FIGS. 8and 8a which are also shown in FIG. 2 are identified in FIGS. 8 and 8agenerally by the same reference numerals as are used in FIG. 2.

As illustrated in FIG. 8, the tool 12 is connected through lead 22 tothe movable contact of a single-pole, double-throw mode switch S1. Oneof the other terminals of switch S4 is coupled to ground and the othercontact is connected to one of the input terminals 142 of an OR-gate150. The OR-gate is connected to one input of an AND-gate 152. An outputof the AND-gate 152 is connected to a set input terminal of a contactsensor flip-flop 154. An output of the flip-flop 154 is connected to asecond input of the AND-gate 152 to provide a set steering signal to theAND gate.

An output of the contact sensor flip-flop 154 is connected to one inputofa four-input AND-gate 156. The other three inputs of the AND-gate 156are respectively connected to receive clock pulses CL, an output signalfrom a gauge mode flip-flop 158, and an output signal from an errordetector flipflop 160.

The gauge mode flip-flop 158 controls the time at which and during whicha calibrating operation is performed. In turn, operation of the gaugemode flip-flop 158 is controlled by output signals from two AND-gates162, 164. The AND-gate 162 has four inputs which are connected toreceive signals from the data input circuitry 90 and an output connectedto a set input terminal of the flip-flop 158. The AND-gate 164 likewisehas four inputs connected to receive signals from the data inputcircuitry 90 and an output connected to a reset input terminal of theflip-flop 158. The same output terminal of the gauge mode flip-flop 158that is connected to an input terminal at the AND-gate 156 is alsoconnected to provide a reset signal to a reset input terminal of thecontact sensor flipflop 154.

The AND-gate 156 previously mentioned has its output connected to oneinput of an inverter 166. The inverter 166 inverts the output signalfrom the AND-gate 156 and provides it to one input of an AND-gate 168.An output of the AND- gate 168 is applied to a set input terminal of apermit gauge transfer flip-flop 170. An output of the permit gaugetransfer flip-flop 170 is connected to a second input of the AND-gate168 to provide a set input steering signal for the AND-gate.

The output of the permit gauge transfer flip-flop 170 is also Iconnected as one input to the OR-gate 118 previously described inconnection with FIG. 6. A second input to the OR-gate 118 is alsoprovided from the AND-gate 116 previously described with reference tothat same figure. Thus, the OR-gate 118 provides an output signal to theAND-gate 120 in the data transfer circuitry in response to receivingeither a normal transfer signal from the AND-gate 116 or a falsetransfer signal from the permit gauge transfer flip-flop 170.

The output of the OR-gate 118 is also connected to one input of anAND-gate 172. An output of the AND-gate 172 is connected to a resetinput terminal of the permit gauge transfer flip-flopl70. A second inputof the AND-gate 172 is connected to receive clock signals CL. The signalfrom the OR-gate 118 to the AND-gate 172 provides a reset steeringsignal for that AND gate.

The error detection portion of the circuitry includes the error detectorflip-flop 160 previously mentioned, which receives a set input signalfrom an OR-gate 174. The OR-gate 174 has two inputs which respectivelyreceive signals from AND-gates 176, 178.

The AND-gate 176 has two inputs, one of which is connected to receive asignal from the gauge mode flip-flop 158 and the other of which isconnected to receive a signal from the AND-gate 116 through an inverter180. The AND-gate 178 also has two inputs, one of which is connected toreceive a signal from the contact sensor flip-flop 154 and the other ofwhich is connected to receive a signal from an OR-gate 182. In turn, theOR-gate 182 receives and inverts a signal from an AND-gate 184. TheAND-gate 184 has two inputs, one of which is connected to receive asignal from the gauge mode flip-flop 157 and the other of which isconnected to receive clock signals CL. The output signal of the errordetector flip-flop 160 is supplied through an inverter 186 todeactivation circuitry 188. The deactivation circuitry 188 serves toimmobilize the machine in response to an error signal from the detectorflipflop 160. It may also serve to energize one or more alarms orannunciators 190 of any desired type to provide a visible or audibleindication of machine malfunction.

In normal operation, signals are provided through the AND- gate 116 andthe OR-gate 118 to initiate a data transfer operation in the datatransfer circuit 96. This has been previously explained in connectionwith FIGS. 6 and 7. When in the calibration mode of operation, a falsesignal is providedthrough the OR-gate 118 which actuates the datatransfer circuit in precisely the same manner as a normal signalprovided through the AND-gate 116. Calibrating operation is initiated byreceipt of gauge mode command signals from the data input circuitry 90by the AND-gate 162. The output signal of the gauge mode flip-flop 158causes the contact sensor flipflop 154 to be reset if it has not beenpreviously reset.

The machine is now commanded to move toward the calibration block 18.When the tool 12 contacts the block 18, the block 18 is brought toground potential through the tool 12 and switch S-l. Since the block 18is connected to one of the input terminals of OR-gate 150, that inputterminal is brought to ground potential. When this input terminal isgrounded, a binary 0 signal is applied to AND-gate 152. Then, a signalis supplied from the AND-gate 152 to the contact sensor 154 to set thatflip-flop. This signal, in turn, provides a logic 0 signal to one inputof the AND-gate 156. The mode flip-flop 158 having been set is alsoproviding a logic 0" signal to another input of the AND-gate 156. In theevent that there is no system error, the error detector flip-flop 160 isalso providing a logic 0" signal to the AND-gate 156. Therefore, whennext a logic 0 clock pulse CL appears, the AND- gate 156 will provide alogic 1" output signal to the inverter 166. The OR gate inverts thatsignal and thus provides a logic 0 signal to one input of the AND-gate168. If the permit gauge transfer flip-flop is in its reset condition,it also'is providing a logic 0" signal to the AND-gate 168. Thus, theAND-gate 168 will provide a logic l signal to set the gauge transferflip-flop 170. This causes the gauge transfer flip-flop 170 to provide alogic l signal to the OR-gate 118. The OR- gate 118 inverts this signaland provides it as a logic 0" signal to the AND-gate 120 in the datatransfer circuit.

The OR-gate 118 also provides a logic 0 signal to one input of theAND-gate 172. Thus, upon receipt of the next logic 0 clock pulse CL, theAND-gate 172 will cause the permit gauge transfer flip-flop 17 0 to bereset.

The contact sensor flip-flop 154 is reset after the calibratingoperation either by the start of a second calibrating operation or bythe provision of a normal transfer signal from the AND- gate 116. Thefirst condition is shown by the connection from the gauge mode flip-flopto the reset terminal of the contact sensor flip-flop 154, whileconnections for the latter resetting operation are not shown.

The gauge mode flip-flop 158 is reset by receipt of signals at theAND-gate 164 from the data input circuitry 90 indicating the start of anormal programming operation.

The error detection portion of the circuitry causes deactivation of themachine under two conditions. These conditions are met by the tooltouching the calibration block when the gauger is not in the calibrationmode of operation, or if when in the calibration mode of operation, anormal transfer signal is provided.

The detection of the former abnormality involves the AND- gate 184, theinverter 182, and the AND-gate 178. If the equipment is not in thecalibration mode of operation, a logic 0 will be provided at one inputof the AND-gate 184 from the gauge mode flip-flop 158. Therefore, at theoccurrence of the next logic 0 clock pulse CL, a signal will be sentthrough the inverter 182 and will appear as a logic 0" signal at oneinput to the AND-gate 178. If the tool touches the calibration block, itwill cause a logic 0 signal to appear at the output of the contactsensor flip-flop 154. This signal is also supplied to the AND-gate 178so that the AND-gate 178 will supply a signal through the OR-gate 174 toset the error detector flipflop 160. When the error detector flip-flop160 is set, it provides a logic l signal to an input of the AND-gate156, so that the gauger is inoperative. Of course, the error detectorflip-flop 160 also provides a signal through the inverter 186 to thedeactivation circuitry 188 to suspend operation of the machine.

If the latter abnormality occurs, it is detected by the ,AND- gate 176.When operating in the calibrating mode, the gauge mode flip-flop 158provides a logic 0 signal to an input of the AND-gate 176. If now anormal transfer should occur, the AND-gate 116 will provide a logic 1"output signal. That signal is inverted by the inverter and supplied as alogic 0 signal to the second input of the gate 176. This causes a signalto be supplied from that AND gate through the OR-gate 174 to set theerror detector flip-flop 160 and suspend operations as previouslydescribed.

Resetting of the error detector flip-flop 160 is accomplished by amanual control (not shown). This insures that the machine malfunction isbrought to the attention of an operator and the condition correctedbefore operation is resumed.

GAUGING MOD E OF OPERATION Having now described the calibration mode ofoperation which is applicable to the'calibration of a machine tool, suchas a cutting tool, as well as to an inspection probe, the operation ofthe gauging mode will now be described. Thus, the description whichfollows is directed toward the gauging of the dimensions ofa workpieceafter the workpiece has been partially or completely machined.

During the gauging mode of operation, tool 12 takes the form of aninspection probe. The inspection probe may be commanded to move tovarious inspection points on the workpiece or ring in order to gauge thedimensions of the inspection points. The mode switch S1 is left in theposition as shown in FIG. 8, and the inspection probe is calibrated inthe same manner as was described with respect to the tool 12. in otherwords, each of the steps which were carried out to calibrate the tool 12is performed again with the inspection probe in order to preciselycalibrate the position of the probe. This calibration procedure isnecessitated by the same factors which necessitate calibrating themachine tool, i.e., misalignment of the tool, wear on the edge of thetool, etc.

Reference is again made to FIGS. 8 and 8a which also include circuitryfor carrying out the function of gauging a workpiece. More particularly,the conductor which connects the permit gauge transfer flip-flop 170 tothe ORgate 118, is also connected to the inputs of a pair of AND-gates200, 202. The output terminals of the ANDgates 200, 202 are respectivelycoupled through a pair of preset circuits 204, 206 to a pair of readoutdevices 208, 210. The readout device 208 provides an X-axis readoutindication and is in turn coupled to an X-axis printer 211, and thereadout device 210 provides a Y- axis readout indication and is in turncoupled to a Y-axis printer 212.

A pair of four-input AND-gates 214, 216 have their input terminalsconnected to the numerical data input circuit 90 and their outputterminals respectively coupled to. the set terminals of a Y-axisinspection flip-flop 218 and an X-axis inspection flip-flop 220. Thereset terminals of flip-flops 218, 220 are connected directly to theoutput terminals of the AND-gate 164. In addition, the output terminalof Y-axis inspection flip-flop 218 is connected to one of the inputterminals of an AND-gate 222 and one of the input terminals of anNAND-gate 224. Similarly, the output terminal of X-axis inspectionflip-flop 220 is connected to one of the input terminals of an AND-gate226 and one of the input terminals ofa NAND-gate 228. The other inputterminals of AND-gates 222, 226 are connected in common to the commonlyconnected input terminals of the AND-gates 200, 202, and the other inputterminals of NAND-gates 224, 228 are connected in common to theconductor which extends between the gauge mode flip-flop 158 and theAND-gate 176.

The output terminals of AND-gates 222, 226 are respectively coupled tothe Y-axis printer 212 and X-axis printer 211. The output terminals ofNAND-gates 224, 228 are respectively connected to the other inputterminals of AND-gates 202, 200, and the function generator 88 isconnected to both the X- axis readout device 208 and the Y-axis readoutdevice 210.

Another pair of four input AND-gates 230, 232, have their inputterminals connected to the numerical data input circuit 90 and theiroutput terminals respectively connected to a Y- axis polarity flip-flop234 and an Xaxis polarity flip-flop 236. The output terminals of theX-polarity flip-flop 236 are connected to the X-readout device 208 andthe output terminals of the Y-polarity flip-flop 234 are connected tothe Y-axis readout device 210.

Once the inspection probe has been calibrated as previously described,the mode switch 8-1 is moved from the position as shown in FIG. 8 to aposition in which the tool or probe 12 is connected to the inputterminal 142 of the OR-gate 150. The probe is then commanded to movetoward the workpiece or ring 10 and toward a preselected point on thering at which the dimension is to be measured. The command signal issomewhat similar to the command signal given to the tool 12 during thecalibrate cycle, i.e., the tool is commanded to move to a positionbeyond the point to be inspected on the ring 10. This point wouldactually be within the ring 10.

- diameter measurement.

Accordingly, in the gauging mode, a particular program is coded on thetape. The tape program commands the probe to move to a position whichwould theoretically require the probe to move past the surface of theworkpiece or ring 10. Upon electrical contact being made between theprobe and the ring 10, a logical l signal is applied to the OR-gate 150.This signal causes the data in the counters to go to a zero count, whichin turn, causes a transfer signal to be generated indicating to thesystem that the commanded position has been reached. This transfersignal, or ffalse" signal, which is generated when the probe reaches afalse" position, actuates the control system to move into the nextsequence of the program.

The X-axis readout device 208 and Y-axis readout device 210 arecalibrated in inches and are controlled by the function generator 88 tocount down for each incremental move of the probe to thereby maintain acontinuous readout of the probe position. The X-axis printer 211 andY-axis printer 212 are responsive to the contact between the probe andthe ring 10 to thereby cause the readout information to be printed onlyupon contact by the probe (not shown).

It is now apparent that the method and apparatus of the invention attainthe general objective set forth. Among the apparent advantages inherentin the use of this invention are the elimination of inspection time dueto more accurate machining, a reduction in the time required forproducing a machined part, and a reduction in the time required to gaugea machined part.

Although one embodiment of the invention has been described andillustrated, it is apparent to one skilled in the art that variouschanges and modifications may be made without departing from the spiritand scope of the invention.

lclaim:

1. A method of calibration positioning a tool in a numericallycontrolled machine tool in which an electrical transfer signal indicatesthat said tool has reached a commanded position, including the steps of:

a. moving said tool toward a predetermined commanded, but unattainable,position through a calibration position; and

b. providing a false electrical transfer signal when an operativeportion of said tool reaches said calibration position in the course ofmoving toward said commanded position.

2. A method of calibration positioning a tool in a numericallycontrolled machine tool in which an electrical transfer signal indicatesthat said tool has reached a commanded position, including the steps of:

a. moving said tool toward a commanded, but unattainable,

position through a calibration position;

b. providing a false electrical transfer signal when an operativeportion of said tool reaches said calibration position in the course ofmoving toward said commanded position; and,

moving said tool to a new commanded position in response to said falsetransfer signal and using said calibration position as a referenceposition.

3. The method of claim 2, further including the step of suspendingoperation of said machine tool when said transfer signal is providedbefore said tool reaches said calibration position.

4. The method of claim 2, further including the step of suspendingoperation of said machine tool when said false transfer signal isprovided while said tool is moving toward a position other than saidcommanded position.

5. The method of claim 2, further including the steps of suspendingoperation of said machine tool when said transfer signal is providedbefore said tool reaches said calibration position, and for suspendingoperation of said machine tool when said false transfer signal isprovided while said tool is moving toward a position other than saidcommanded position.

6. A method of calibration positioning a tool in a numericallycontrolled machine tool in which an electrical transfer signal indicatesthat said tool has reached a commanded position in terms of toolposition coordinates, comprising the steps of:

a. providing a gauge having a surface whose position in one of saidcoordinates is known;

b. positioning said tool adjacent said surface;

c. moving said tool along one of said coordinates toward said surface toa commanded position past said surface;

d. causing a false electrical transfer signal to be provided when anoperative portion of said tool contacts said surface; and

e. moving said tool away from said surface in response to said falsetransfer signal to a new commanded position in said one of saidcoordinates using said position of said surface in said one of saidcoordinates as a reference posi- 7. The method of claim 6, furtherincluding the step of suspending operation of said machine tool whensaid transfer signal is provided before said tool reaches saidcalibration position.

8. The method of claim 6, further including the step of suspendingoperation of said machine tool when said false transfer signal isprovided while said tool is moving toward a position other than saidcommanded position.

9. The method of claim 6, further including the steps of suspendingoperation of said machine tool when said transfer signal is providedbefore said tool reaches said calibration position and for suspendingoperation of said machine tool when said false transfer signal isprovided while said tool is moving toward a position other than saidcommanded position.

10. A method of calibration positioning a numerically controlledmachinein which an electrical transfer signal indicates that an element hasreached a predetermined commanded position, including the steps of:

a. moving said element toward a commanded, but unattainable, positionthrough a calibration position; and

b. providing a false electrical transfer signal when said elementreaches said calibration position in the course of moving toward saidcommanded position.

11. The method of claim 10, further including the step of moving saidelement to a new commanded position in response to said false transfersignal and using said calibration position as a reference position.

12. The method of claim 11, further including the step of suspendingoperation of said machine when said transfer signal is provided beforesaid element reaches said calibration position.

13. The method of claim 11, further including the step of suspendingoperation of said tool when said false transfer signal is provided whilesaid element is moving toward a position other than said commandedposition.

14. The method of claim 11, further including the steps of suspendingoperation of said machine when said transfer signal is provided beforesaid element reaches said calibration position, and for suspendingoperation of said machine when said false transfer signal is providedwhile said element is moving toward a position other than said commandedposition.

15. Apparatus for calibration positioning a tool in a numericallycontrolled machine tool in which an electrical transfer signal indicatesthatsaid tool has reached a predetermined commanded position,Comprising:

a. drive means for moving said tool toward said commanded position; andb. electrical means for providing a false electrical transfer signalwhen an operative edge of said tool reaches a calibration position inthe course of moving toward said commanded position.

16. Apparatus for calibration positioning a tool in a numericallycontrolled machine tool in which an electrical transfer signal indicatesthat said tool has reached a commanded position, comprising:

a. drive means for moving said tool toward said commanded position;

electrical means for providing a false electrical transfer signal whenan operative edge of said tool reaches a calibration position in thecourse of moving toward said commanded position; and,

c. control means for actuating said drive means in response to saidfalse transfer signalto move said tool away from said calibrationposition to a new commanded position using said calibration position asa reference position.

17. The apparatus of claim 16, further including error-detecting meansfor deactivating said drive means when said transfer signal is providedbefore said tool reaches said calibration position.

18. The apparatus of claim 16, further including error-detecting meansfor deactivating said drive means when said false transfer signal isprovided while said tool is moving toward a position other than saidcommanded position.

19. The apparatus of claim 16, further including error-detecting meansfor deactivating said drive means when said transfer signal is providedbefore said tool reaches said calibration position, and for deactivatingsaid drive means when said false transfer signal is provided while saidtool is moving toward a position other than said commanded position.

20. Apparatus for calibration positioning a tool in a numericallycontrolled machine tool in which an electrical transfer signal indicatesthat said tool has reached a commanded position, comprising:

a a gauge having a surface whose position is known in terms of toolposition coordinates; drive means for moving said tool along one of saidcoordinates toward said surface to a commanded position past saidsurface;

c. electrical means in circuit with'said gauge and'said tool forproviding a false electrical transfer signal when an operative portionof said tool contacts said surface; and control means for actuating saiddrive means in response to said false transfer signal to move said toolaway from said surface to a new commanded position in said one of saidcoordinates using said position of said surface in said one of saidcoordinates as a reference position.

21. The apparatus of claim 20, further including error-detecting meansfor deactivating said drive means when said transfer signal is providedbefore said tool contacts said surface.

22. The apparatus of claim 20, further including error-detecting meansfor deactivating said drive means when said tool contacts said gaugewhile said tool is moving toward a positio other than said commandedposition. 1

23. The apparatus of claim 20, further including error-detecting meansfor deactivating said drive means when said transfer signal is providedbefore said tool contacts said surface, and for deactivating said drivemeans when said tool contacts said gauge while said tool is movingtoward a position other than said commanded position.

24. Apparatus for calibration positioning a numerically controlledmachine in which an electrical transfer signal indicates that an elementhas reached a predetermined commanded position, comprising:

a. drive means for moving said element toward said commanded position;and

b. electrical means for providing a false electrical transfer signalwhen an operative edge of said element reaches a calibration position inthe course of moving toward said commanded position.

false transfer signal is provided while said element is moving toward aposition other than said commanded position.

28. The apparatus of claim 24, further including error-detecting meansfor deactivating said drive means when said transfer signal is providedbefore said element reaches said calibration position, and fordeactivating said drive means when said false transfer signal isprovided while said element is moving toward a position other than saidcommanded position.

1. A method of calibration positioning a tool in a numericallycontrolled machine tool in which an electrical transfer signal indicatesthat said tool has reached a commanded position, iNcluding the steps of:a. moving said tool toward a predetermined commanded, but unattainable,position through a calibration position; and b. providing a falseelectrical transfer signal when an operative portion of said toolreaches said calibration position in the course of moving toward saidcommanded position.
 2. A method of calibration positioning a tool in anumerically controlled machine tool in which an electrical transfersignal indicates that said tool has reached a commanded position,including the steps of: a. moving said tool toward a commanded, butunattainable, position through a calibration position; b. providing afalse electrical transfer signal when an operative portion of said toolreaches said calibration position in the course of moving toward saidcommanded position; and, c. moving said tool to a new commanded positionin response to said false transfer signal and using said calibrationposition as a reference position.
 3. The method of claim 2, furtherincluding the step of suspending operation of said machine tool whensaid transfer signal is provided before said tool reaches saidcalibration position.
 4. The method of claim 2, further including thestep of suspending operation of said machine tool when said falsetransfer signal is provided while said tool is moving toward a positionother than said commanded position.
 5. The method of claim 2, furtherincluding the steps of suspending operation of said machine tool whensaid transfer signal is provided before said tool reaches saidcalibration position, and for suspending operation of said machine toolwhen said false transfer signal is provided while said tool is movingtoward a position other than said commanded position.
 6. A method ofcalibration positioning a tool in a numerically controlled machine toolin which an electrical transfer signal indicates that said tool hasreached a commanded position in terms of tool position coordinates,comprising the steps of: a. providing a gauge having a surface whoseposition in one of said coordinates is known; b. positioning said tooladjacent said surface; c. moving said tool along one of said coordinatestoward said surface to a commanded position past said surface; d.causing a false electrical transfer signal to be provided when anoperative portion of said tool contacts said surface; and e. moving saidtool away from said surface in response to said false transfer signal toa new commanded position in said one of said coordinates using saidposition of said surface in said one of said coordinates as a referenceposition.
 7. The method of claim 6, further including the step ofsuspending operation of said machine tool when said transfer signal isprovided before said tool reaches said calibration position.
 8. Themethod of claim 6, further including the step of suspending operation ofsaid machine tool when said false transfer signal is provided while saidtool is moving toward a position other than said commanded position. 9.The method of claim 6, further including the steps of suspendingoperation of said machine tool when said transfer signal is providedbefore said tool reaches said calibration position and for suspendingoperation of said machine tool when said false transfer signal isprovided while said tool is moving toward a position other than saidcommanded position.
 10. A method of calibration positioning anumerically controlled machine in which an electrical transfer signalindicates that an element has reached a predetermined commandedposition, including the steps of: a. moving said element toward acommanded, but unattainable, position through a calibration position;and b. providing a false electrical transfer signal when said elementreaches said calibration position in the course of moving toward saidcommanded position.
 11. The method of claim 10, further including thestep of moving said element to a new commanded poSition in response tosaid false transfer signal and using said calibration position as areference position.
 12. The method of claim 11, further including thestep of suspending operation of said machine when said transfer signalis provided before said element reaches said calibration position. 13.The method of claim 11, further including the step of suspendingoperation of said tool when said false transfer signal is provided whilesaid element is moving toward a position other than said commandedposition.
 14. The method of claim 11, further including the steps ofsuspending operation of said machine when said transfer signal isprovided before said element reaches said calibration position, and forsuspending operation of said machine when said false transfer signal isprovided while said element is moving toward a position other than saidcommanded position.
 15. Apparatus for calibration positioning a tool ina numerically controlled machine tool in which an electrical transfersignal indicates that said tool has reached a predetermined commandedposition, Comprising: a. drive means for moving said tool toward saidcommanded position; and b. electrical means for providing a falseelectrical transfer signal when an operative edge of said tool reaches acalibration position in the course of moving toward said commandedposition.
 16. Apparatus for calibration positioning a tool in anumerically controlled machine tool in which an electrical transfersignal indicates that said tool has reached a commanded position,comprising: a. drive means for moving said tool toward said commandedposition; b. electrical means for providing a false electrical transfersignal when an operative edge of said tool reaches a calibrationposition in the course of moving toward said commanded position; and, c.control means for actuating said drive means in response to said falsetransfer signal to move said tool away from said calibration position toa new commanded position using said calibration position as a referenceposition.
 17. The apparatus of claim 16, further includingerror-detecting means for deactivating said drive means when saidtransfer signal is provided before said tool reaches said calibrationposition.
 18. The apparatus of claim 16, further includingerror-detecting means for deactivating said drive means when said falsetransfer signal is provided while said tool is moving toward a positionother than said commanded position.
 19. The apparatus of claim 16,further including error-detecting means for deactivating said drivemeans when said transfer signal is provided before said tool reachessaid calibration position, and for deactivating said drive means whensaid false transfer signal is provided while said tool is moving towarda position other than said commanded position.
 20. Apparatus forcalibration positioning a tool in a numerically controlled machine toolin which an electrical transfer signal indicates that said tool hasreached a commanded position, comprising: a. a gauge having a surfacewhose position is known in terms of tool position coordinates; b. drivemeans for moving said tool along one of said coordinates toward saidsurface to a commanded position past said surface; c. electrical meansin circuit with said gauge and said tool for providing a falseelectrical transfer signal when an operative portion of said toolcontacts said surface; and d. control means for actuating said drivemeans in response to said false transfer signal to move said tool awayfrom said surface to a new commanded position in said one of saidcoordinates using said position of said surface in said one of saidcoordinates as a reference position.
 21. The apparatus of claim 20,further including error-detecting means for deactivating said drivemeans when said transfer signal is provided before said tool contactssaid surface.
 22. The apparatus of claim 20, further includingerror-detectIng means for deactivating said drive means when said toolcontacts said gauge while said tool is moving toward a position otherthan said commanded position.
 23. The apparatus of claim 20, furtherincluding error-detecting means for deactivating said drive means whensaid transfer signal is provided before said tool contacts said surface,and for deactivating said drive means when said tool contacts said gaugewhile said tool is moving toward a position other than said commandedposition.
 24. Apparatus for calibration positioning a numericallycontrolled machine in which an electrical transfer signal indicates thatan element has reached a predetermined commanded position, comprising:a. drive means for moving said element toward said commanded position;and b. electrical means for providing a false electrical transfer signalwhen an operative edge of said element reaches a calibration position inthe course of moving toward said commanded position.
 25. The apparatusof claim 24, further including control means for actuating said drivemeans in response to said false transfer signal to move said elementaway from said calibration position to a new commanded position usingsaid calibration position as a reference position.
 26. The apparatus ofclaim 24, further including error-detecting means for deactivating saiddrive means when said transfer signal is provided before said elementreaches said calibration position.
 27. The apparatus of claim 24,further including error-detecting means for deactivating said drivemeans when said false transfer signal is provided while said element ismoving toward a position other than said commanded position.
 28. Theapparatus of claim 24, further including error-detecting means fordeactivating said drive means when said transfer signal is providedbefore said element reaches said calibration position, and fordeactivating said drive means when said false transfer signal isprovided while said element is moving toward a position other than saidcommanded position.